Method and apparatus for manufacturing a crimped sheet of material

ABSTRACT

The invention relates to an apparatus (1) for crimping a sheet of material (7), the apparatus (1) comprising: a first and a second facing crimping rollers (4,5) defining a first and a second rotation axis, wherein at least one of the first and second crimping roller (4,5) includes: a plurality of ridges (9), each ridge (9) defining a first and a second flank (16) and a tip, the first or the second flank (16) forming a flank angle (15) with a radial direction passing through the tip, the flank angle (15) being comprised between about 8 degrees and about 10 degrees.

The invention concerns an apparatus for crimping a sheet of material and the manufacturing process of a crimped sheet of material, the crimped sheet of material preferably used in the production of an aerosol-generating article.

Typically, aerosol-generating articles comprise a plurality of elements assembled in the form of a rod. The plurality of elements generally includes an aerosol-forming substrate and a filter element. One or both of the filter and the aerosol-forming substrate may comprise a plurality of channels to provide air-flow through the rod. The plurality of channels may be provided by crimping a sheet of material and consequently gathering the material within the rod to form the channels. In such examples, the crimped sheet is generally formed by crimping a substantially continuous web and cutting a plurality of crimped sheets from the crimped and gathered web.

This material to be crimped, that is the continuous web, in the field of aerosol generating articles, can be tobacco cast leaves (TCL), polylactic acid (PLA), tow or others. Methods and apparatuses for manufacturing a crimped web for use in an aerosol-generating article are known in the art. Known methods of manufacturing a crimped web generally involve feeding a substantially continuous web between a pair of interleaved rollers to apply a plurality of longitudinally extending crimp corrugations to the continuous web. The crimped web is subsequently gathered to form a continuous rod having a plurality of axial channels. The rod is then wrapped and cut into smaller segments to form an aerosol-generating substrate or filter for an aerosol generating article.

The crimping process creates various effects to the material which is pressed between the crimping rollers.

A first range of effects is related to the manufacturing processes, such as for example the fact that a crimped material can be easily compressed into a rod that will then fit into the aerosol-generating articles.

Once the crimped material is compressed into a rod and added to the aerosol-generating article, a second range of effects is related to the crimping, such as the users' smoking experience. More specifically, the crimping process affects the air contact between the air, penetrating the aerosol-generating article, and the crimped sheet of material, and the resistance to draw (RTD).

The crimping process is therefore important for a correct manufacturing of the article and for obtaining the desired smoking experience.

However, a non-optimal or sub-optimal crimping process could weaken the crimped web of material, could deteriorate the release of substances from the crimped sheet of material to the penetrating air of the rod, as well as adversely affect the RTD (resistance to draw) value.

It would be desirable to provide a method and an apparatus for manufacturing a crimped sheet of material, preferably for an aerosol-generating article, that allows to have a better control and an increased flexibility on the aerosol-generating articles' properties which are related to the crimping process.

According to a first aspect of the present invention, an apparatus for crimping a sheet of material is provided, the apparatus comprising a first and a second facing crimping rollers defining a first and a second rotation axis, wherein at least one of the first and second crimping roller includes a plurality of ridges, each ridge defining a first and a second flank and a tip, the first or the second flank forming a flank angle with a radial direction passing through the tip, the flank angle being comprised between about 8 degrees and about 10 degrees.

Preferably, the flank angle is comprised between about 4 degrees and about 20 degrees.

So far, the optimization of the crimping process was done with the object of gaining an improved experience for the end-consumer, in particular with a focus of getting a particularly suitable RTD value and a good release of the substances to be released by the aerosol-generating article. This resulted in a sometimes particularly bad and error prone production technique, in particular for the crimping step. Here, in production methods according to the state of the art, quite often a deterioration of the quality of the crimped sheet of material was present. Even a shredding of the sheet of material may have been observed in the course of the crimping process. This was not only disadvantageous for the production in that a maintenance shutdown of the production apparatuses was necessary quite frequently and sometimes even at unforeseeable times. Furthermore, such a shredding or decreased quality of the crimped sheet of material could even lead to a lower smoking experience for the end consumer, for example by a varying RTD. Using the present invention, the crimped sheet of material may be significantly less prone to any damages or otherwise adverse alterations of the sheet of material. At the same time, a particularly advantageous smoking experience for the end consumer may be provided.

The two rotation axis of the rollers may be aligned essentially parallel to each other or my show a certain and preferably small finite angle between them.

As used herein, the term “sheet” denotes a laminar element having a width and length that is substantially greater than the thickness thereof.

As used herein, the term “crimped” denotes a sheet or web with a plurality of corrugations. The term “crimping” denotes the formation of a crimped sheet of material, preferably from an essentially flat sheet of material or a previously untreated sheet of material with respect of generating a structured surface.

As used herein, the term “pitch value” or “pitch” refers to the lateral distance between the troughs at either side of the peak of a particular corrugation or to the lateral distance between two neighbouring or successive peaks or ridges.

As used herein, the term “amplitude value” or “amplitude” refers to the height of a corrugation from its peak to the deepest point of the deepest directly adjacent trough.

As used herein, the term “ridge” denotes a protrusion as seen in an outward or inward radial direction as seen from the axis of rotation of the respective roller, thus forming a tip that may be either of a corner-type shape or of a rounded shape. The respective tip may be limited by two flanks, one on each side of the tip. The ridge or tip may have a certain extent along the surface of the roller, when seen in a tangential direction. Also a ridge, as the corrugations, define an amplitude in the same manner. Between two ridges a “trough” is present.

The flank has a direction given by its tangent. With “flank angle” the angle formed between the tangent to the flank and a radial direction passing through the tip of the ridge is considered. The radial direction can be visualized as a radius of the roller connecting the center of the crimping roller (where the rotation axis of the roller is present) and the tip of the ridge.

Because more than one tangent may be present, the term “flank angle” is defined with respect to the minimum or maximum value of a local flank angle when going along the shape of the surface of the roller between two successive tips or between a tip and a trough bottom. The trough's bottom may be the position where the smallest local radius of the roller is defined between two neighbouring tips. The minimum or maximum value of the angle may relate to the magnitude of the respective value. However, another pronounced or well defined position along the surface of a flank may be used for defining the flank angle as well.

The ridges may be symmetrical about the rotation axis of the respective roller, so that the flanks on the opposite sides of a tip may be symmetrical. In particular in this case, the angle between two flanks forming the same ridge is twice any of the two flank angles. Alternatively, one or more of the ridges may be asymmetrical about the rotation axis of the respective roller. That is, the flank angles of both flanks of a ridge may be different. This statement can relate to a certain portion of the roller (so that at least two surface areas of a roller are different), or to several or even to a majority of portions of the roller.

As used herein, the term “ridge angle” refers to the angle between the ridge and a longitudinal direction.

As used herein, the term “corrugations” denotes a plurality of substantially parallel ridges formed from alternating peaks and troughs joined by corrugation flanks. They can are formed in a sheet by the ridges of crimping rollers. The rollers may also have corrugations, formed by a plurality of adjacent ridges. The corrugations may have many different shapes; this includes, but is not limited to, corrugations having a rhomboid-like profile, sinusoidal wave profile, triangular profile, sawtooth profile, or any combination thereof.

As used herein, the definitions with respect to the dimensions and shapes of the ridges, amplitudes, pitches, tips, flanks and the like may be understood with respect to the rollers of the crimping apparatus. Preferably, the resulting crimped sheet of material may show at least in part essentially the same dimensions and shapes in its corrugations. However, certain deviations may be present as well. In particular certain material properties of the sheet of material to be crimped may result in deviations from the shape or dimensions of one or both of the rollers.

As used herein, the term “substantially interleave” denotes that the corrugations of the first and second rollers at least partially mesh. This includes arrangements in which the corrugations of one or both of the rollers are symmetrical or asymmetrical. The corrugations of the rollers may be substantially aligned, or at least partially offset. The peak of one or more ridges of the first or second rollers may interleave with the trough between two ridges of the other of the first and second rollers. Preferably, the corrugations of the first and second rollers interleave such that substantially all of the corrugation troughs of one of the first and second rollers each receive a single corrugation peak of the other of the first and second rollers.

As used herein, the term “longitudinal direction” refers to a direction extending along, or parallel to, the length of a web or sheet.

As used herein, the term “rotation axis” refers to a direction extending along, or parallel to, a line that does essentially show no translational movement when the respective roller is rotated during its normal state of operation. This may be referred as to the axis of the respective roller.

As used herein, the term “width” refers to a direction perpendicular to the length of a web or sheet, or in the case of a roller, parallel to the axis of the roller.

As used herein, the term “rod” denotes a generally cylindrical element of substantially circular or oval cross-section.

As used herein, the terms “axial” or “axially” refer to a direction extending along, or parallel to, the cylindrical axis of a rod.

As used herein, the terms “gathered” or “gathering” denote that a web or sheet is convoluted, or otherwise compressed or constricted substantially transversely to the cylindrical axis of the rod.

As used herein, the term “section” of roller denotes a certain area on the outer circumferential surface of at least one of the rollers. The limitation of the surface may be defined in terms of a certain extent along the axial direction of the respective roller (which is parallel to the rotation axis of the respective roller). Additionally or alternatively the limitation may be defined in terms of a certain extent along the tangential direction of the respective roller (defining a certain angular extent).

An aerosol-generating article may be a heated aerosol-generating article, which is an aerosol-generating article comprising an aerosol-forming substrate that is intended to be heated rather than combusted in order to release volatile compounds that can form an aerosol. A heated aerosol-generating article may comprise an on-board heating means forming part of the aerosol-generating article, or may be configured to interact with an external heater forming part of a separate aerosol-generating device.

In order to produce a crimped sheet of material, the sheet of material, which can be for example tow, PLA or a sheet formed by an alkaloid containing material, such as a homogenised tobacco material, is transported along a transport direction. The transport can be performed by any suitable means, for example by pulling via rollers, in particular by pulling using said first and second crimping roller. During the transport, the sheet or web of material passes through a so-called “nip” that is formed between a first and a second crimping roller.

At least one of the rollers, either the first or the second or both includes ridges, which come into contact with the sheet of material so that corresponding corrugations are formed onto the sheet when it passes through the nip.

Both the first and the second crimping rollers may show a plurality of ridges or corrugations. In particular in this case, the rollers may be designed an arranged in a way that at least parts of them do substantially interleave.

Alternatively, only one of the first and second rollers may show corrugations, the other roller showing an essentially smooth cylindrical surface.

Both the first and second rollers may both show corrugations, but in non-corresponding portions, that is for each portion of the sheet of material which comes into contact with the rollers, only one of the first and second roller forms crimp corrugations on that portion of the sheet.

Each ridge includes two flanks terminating in a tip of the ridge. At least one of the flanks form a flank angle with respect to a radial direction, that is a direction along a radius of the roller starting from the rotational axis of the same, which is comprised between about 4 degrees and about 20 degrees, preferably between about 8 and about 10 degrees. The flank angle is the angle between a tangent of the flank where the flank includes a linear portion and the radial direction defined above.

Preferably, all ridges of the first or of the second roller form such a flank angle.

Even more preferably, both flanks of each ridge form a flank angle within this range.

Tests have shown that ridges forming flank angles within the claimed range reduce the phenomenon of shredding and possibly also reduce damages on the sheet of material passing into the hip between the rollers. Therefore, an improved control of the crimping process is possible.

Preferably, the ridges are distanced one to the other with a constant pitch. This statement might apply to essentially the whole outer circumferential surface of the first or second roller. This statement may apply to essentially the complete outer circumferential surface of the rollers, in particular with respect to the width, the circumference or both of the respective roller. However, it is possible that the first or second roller show several sections, and the constant pitch occurs only within the respective section. The crimped sheet of material that is crimped using such rollers may show particularly advantageous properties, and may possibly show a particularly advantageous RTD.

Advantageously, the ridges have all substantially the same amplitude. This statement may apply to essentially the complete outer circumferential surface of the rollers, in particular with respect to the width, the circumference or both of the respective roller. However, it is possible that the first or second roller show several sections, and the same amplitude occurs only within the respective section. The crimped sheet of material that is crimped using such rollers may show particularly advantageous properties, in particular when it comes to gathering the crimped sheet of material.

Preferably, the first and second flanks are symmetrical with respect to the radial direction passing through the tip. This statement may apply to essentially the complete outer circumferential surface of the rollers, in particular with respect to the width, the circumference or both of the respective roller. Using such rollers, the sheet of material to be crimped may be less prone to shredding or other adverse alterations. Thus, the corresponding apparatus might be particularly preferred.

Even more preferred, the first or the second roller is realised in metal. Of course, both rollers can be realised in metal as well. Such a design of the rollers may result in a particularly long lifetime of a rollers and the apparatus they are the used in.

Preferably, said flank angle is comprised between about 8 degrees and about 10 degrees. This statement may apply to essentially the complete outer circumferential surface of the rollers, in particular with respect to the width, the circumference or both of the respective roller. Using such dimensions, an apparatus showing a particularly low tendency towards shredding of the sheet of material to be crimped may be achieved. In addition, the smoking experience of the end-user of the final product may be particularly high. It is possible that these dimensions are only used in a certain section or in certain sections of the surface of the first or second roller.

Even more preferred, the other of the first and second crimping roller includes a plurality of ridges, the first and second roller being arranged such that the ridges of the first roller substantially interleave with the ridges of the second roller. This statement may apply to essentially the complete outer circumferential surface of the rollers, in particular with respect to the width, the circumference or both of the respective roller. Likewise, the statement might apply to only certain sections of the outer circumferential surface of the rollers. Using such a design, the resulting crimped sheet of material may show a shape that is particularly advantageous with respect to achieving a desired RTD or with respect to the release of a desired amount of volatile compounds when used in the final product.

According to a second aspect of the invention, a method of manufacturing a crimped sheet for an aerosol-generating article is provided, the method comprising the steps of: feeding a substantially continuous sheet of material to a set of crimping rollers, the set of rollers comprising a first roller and a second roller, at least one of the first or second roller including a plurality of ridges; and crimping the substantially continuous web to form the crimped web by feeding the substantially continuous sheet between the first and second rollers in a longitudinal direction of the sheet of material such that the ridges of the first or second rollers apply a plurality of crimp corrugations to the substantially continuous sheet of material, wherein the ridges in the first or second roller defines a first and a second flank and a tip, the first or the second flank forming a flank angle with a radial direction passing through the tip, the flank angle being comprised between about 8 degrees and about 10 degrees.

The method may be realised particularly well, when using an apparatus according to the previous suggestion. When a method according to the present aspect of the invention is employed, similar effects and advantages as previously described in connection with the above described apparatus for crimping a sheet of material may be realised, at least in analogy. Additionally, the method may be modified in the previously described sense as well, at least in analogy. When employing such modifications, similar effects and advantages may be realised in connection with the method as well, at least in analogy.

In particular, it is possible to modify the method in a way that the method comprises the steps of manufacturing a crimped sheet as previously suggested, further comprising the steps of gathering the crimped sheet to form a continuous rod; and cutting the continuous rod into a plurality of rod-shaped components, each rod-shaped component having a gathered crimped sheet formed from a cut portion of the crimped sheet, the crimp corrugations of the crimped sheet defining a plurality of channels in the rod-shaped component.

This way, an aerosol-generating article that suits the present-day market needs may be realised in an efficient and cheap way. In particular, an aerosol-generating article may be realised that resembles a traditional combustion-type aerosol-generating product, in particular a traditional cigarette. The “gathering” can particularly involve the previously described gathering methods. In particular, the “gathering” may comprise a folding process where two portions of the crimped sheet of material can be put on top of each other by a folding-type operation along a usually straight line, or a rolling operation, where the initially ungathered, crimped sheet of material is brought into some kind of a coil-like form. Possibly, a combination of folding and rolling processes may be used as well, where usually a folding-type operation is performed prior to a rolling operation.

Preferably, the method may be used in a way that the sheet of material is one of a sheet of alkaloid containing material, a plastic sheet or a sheet including cellulose. For such sheets, the presently proposed method may be particularly suited. Preferably, the sheet of alkaloid containing material includes a homogenised tobacco sheet.

An “alkaloid containing material” is a material which contains one or more alkaloids. Among alkaloids, nicotine is a preferred one, which can be found in tobacco.

Alkaloids are a group of naturally occurring chemical compounds that mostly contain basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar structure are also termed alkaloids. In addition to carbon, hydrogen and nitrogen, alkaloids may also contain oxygen, sulphur and, more rarely, other elements such as chlorine, bromine, and phosphorus.

Alkaloids are produced by a large variety of organisms including bacteria, fungi, plants, and animals. They can be purified from crude extracts of these organisms by acid-base extraction. Caffeine, nicotine, theobromine, atropine, tubocurarine are examples of alkaloids.

As used herein, the term “homogenised tobacco material” denotes material formed by agglomerating particulate tobacco, which contains the alkaloid nicotine.

A crimped sheet of material that was crimped in the above-described sense may be used for an aerosol-generating article comprising a rod formed from a gathered crimped sheet that was produced in the previously described way.

Such an aerosol-generating article may resemble a combustible smoking article, such as a cigarette. An aerosol-generating article may comprise tobacco. An aerosol-generating article may be disposable. An aerosol-generating article may alternatively be partially-reusable and comprise a replenishable or replaceable aerosol-forming substrate.

As used herein, the term “homogenised tobacco material” denotes material formed by agglomerating particulate tobacco.

A homogenised tobacco material may be in the form of a sheet. The homogenised tobacco material may have an aerosol-former content of greater than 5 percent on a dry weight basis. The homogenised tobacco material may alternatively have an aerosol former content of between about 5 percent and about 30 percent by weight on a dry weight basis. Sheets of homogenised tobacco material may be formed by agglomerating particulate tobacco obtained by grinding or otherwise comminuting one or both of tobacco leaf lamina and tobacco leaf stems; alternatively, or in addition, sheets of homogenised tobacco material may comprise one or more of tobacco dust, tobacco fines and other particulate tobacco by-products formed during, for example, the treating, handling and shipping of tobacco. Sheets of homogenised tobacco material may comprise one or more intrinsic binders, that is tobacco endogenous binders, one or more extrinsic binders, that is tobacco exogenous binders, or a combination thereof to help agglomerate the particulate tobacco; alternatively, or in addition, sheets of homogenised tobacco material may comprise other additives including, but not limited to, tobacco and non-tobacco fibres, aerosol-formers, humectants, plasticisers, flavourants, fillers, aqueous and nonaqueous solvents and combinations thereof. The aerosol-forming substrate may be a solid aerosol-forming substrate. Alternatively, the aerosol-forming substrate may comprise both solid and liquid components. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may further comprise an aerosol former. Examples of suitable aerosol formers are glycerine and propylene glycol. If the aerosol-forming substrate is a solid aerosol-forming substrate, the solid aerosol-forming substrate may comprise, for example, one or more of: powder, granules, pellets, shreds, spaghettis, strips or sheets containing one or more of: herb leaf, tobacco leaf, fragments of tobacco ribs, reconstituted tobacco, homogenised tobacco, extruded tobacco and expanded tobacco. The solid aerosol-forming substrate may be in loose form, or may be provided in a suitable container or cartridge. For example, the aerosol-forming material of the solid aerosol-forming substrate may be contained within a paper or other wrapper and have the form of a plug. Where an aerosol-forming substrate is in the form of a plug, the entire plug including any wrapper is considered to be the aerosol-forming substrate.

Optionally, the solid aerosol-forming substrate may contain additional tobacco or non-tobacco volatile flavour compounds, to be released upon heating of the solid aerosol-forming substrate. The solid aerosol-forming substrate may also contain capsules that, for example, include the additional tobacco or non-tobacco volatile flavour compounds and such capsules may melt during heating of the solid aerosol-forming substrate.

Optionally, the solid aerosol-forming substrate may be provided on or embedded in a thermally stable carrier. The carrier may take the form of powder, granules, pellets, shreds, spaghettis, strips or sheets. The solid aerosol-forming substrate may be deposited on the surface of the carrier in the form of, for example, a sheet, foam, gel or slurry. The solid aerosol-forming substrate may be deposited on the entire surface of the carrier, or alternatively, may be deposited in a pattern in order to provide a non-uniform flavour delivery during use. In certain embodiments, at least part of the aerosol-forming substrate is formed from a gathered crimped sheet according to any of the embodiments described above. In such embodiments, the gathered crimped sheet may comprise a sheet of homogenised tobacco material. In certain embodiments, at least part of the aerosol-forming substrate is deposited on the surface of a carrier in the form of a gathered crimped sheet according to any of the embodiments described above.

The elements of the aerosol-generating article are preferably assembled by means of a suitable wrapper, for example a cigarette paper. A cigarette paper may be any suitable material for wrapping components of an aerosol-generating article in the form of a rod. Preferably, the cigarette paper holds and aligns the component elements of the aerosol-generating article when the article is assembled and holds them in position within the rod. Suitable materials are well known in the art.

Preferably, the aerosol-forming substrate is formed from or comprises a homogenised tobacco material having an aerosol former content of greater than 5 percent on a dry weight basis and water. For example, the homogenised tobacco material may have an aerosol former content of between 5 percent and 30 percent by weight on a dry weight basis. An aerosol generated from such aerosol-forming substrates may be perceived by a user to have a particularly high temperature and the use of a high surface area, low resistance to draw aerosol-cooling element may reduce the perceived temperature of the aerosol to an acceptable level for the user.

The aerosol-generating article may be substantially cylindrical in shape. The aerosol-generating article may be substantially elongate. The aerosol-generating article may have a length and a circumference substantially perpendicular to the length. The aerosol-forming substrate may be substantially cylindrical in shape. The aerosol-forming substrate may be substantially elongate. The aerosol-forming substrate may also have a length and a circumference substantially perpendicular to the length. The aerosol-forming substrate may be received in the aerosol-generating device such that the length of the aerosol-forming substrate is substantially parallel to the airflow direction in the aerosol-generating device. The aerosol-cooling element may be substantially elongate.

The aerosol-generating article may have a total length between approximately 30 millimeters and approximately about 100 millimeters. The aerosol-generating article may have an external diameter between approximately about 5 millimeters and approximately about 12 millimeters.

The aerosol-generating article may comprise a filter or mouthpiece. The filter may be located at the downstream end of the aerosol-generating article. The filter may be a cellulose acetate filter plug. The filter is approximately about 7 millimeters in length in one embodiment, but may have a length of between approximately about 5 millimeters and approximately about 10 millimeters. The aerosol-generating article may comprise a spacer element located downstream of the aerosol-forming substrate.

According to a third aspect, the invention relates to a crimped sheet realized according to the second aspect. The crimped sheet of the invention is more pliable when it comes to gathering and it is less prone to shredding.

Preferably, the crimped sheet of material is one of: a sheet of alkaloid containing material, a plastic sheet or a sheet including cellulose. Preferably, the sheet of alkaloid containing material includes a homogenised tobacco sheet.

According to a fourth aspect, the invention relates to an aerosol generating article comprising a portion of the crimped sheet realized according to the third aspect.

Further advantages of the invention will become apparent from the detailed description thereof with non-limiting reference to the appended drawings:

FIG. 1 is a schematic lateral view of an apparatus for manufacturing of a crimped sheet of material;

FIG. 2 is a schematic front view of the crimping pair of rollers and the nip they are forming for crimping the material; and

FIG. 3 is a schematic partial view of the crimping teeths' geometry of the crimping pair of rollers.

In FIG. 1, the basic layout for an apparatus 1 for manufacturing a crimped sheet of material 7 for an aerosol-generating device is shown in a schematic lateral view.

The raw material is supplied by means of a first coil, namely a supply coil 2. On the supply coil 2, an “endless” sheet of a flat and thin layer of material 3 to be crimped using the apparatus 1 is provided. The material 3 may be a homogenised tobacco sheet or a plastic sheet or a cellulose-type sheet, on which some type of tobacco-like flavour compound may be applied. It is to be understood that the sheet of material 3 that is wound up on coil 2 is strictly speaking not endless. However, the overall length of the sheet of material can be several hundred metres and is therefore much longer than its width. Furthermore, it is possible that a handover mechanism between two consecutive supply coils 2 (not shown) is provided so that a continuous crimping process will be possible.

The sheet is coiled down from the supply coil 2 and enters the “main part” of the apparatus 1, where the processing of the material 3 is performed. The material 3 is fed into the apparatus 1 as a single, flat layer of material 3. The processing of the flat layer of material 3 is done in a nip 6 which is formed between the upper roller 4 and the roller 5 by an appropriate placement of the two rollers 4, 5 at a certain distance. The width of the nip 6 is roughly in the range of the thickness of the entering layer of material 3. The width of the nip 6 is usually defined as the distance to a neighbouring surface portion of the other roller 4, 5 in a direction that is essentially perpendicular to the surface portion in question. Depending on the current necessities of the processing process, the width of the nip 6 is typically slightly smaller than the thickness of the entering layer of material 3, so that the entering layer of material 3 is slightly compressed in the nip 6. Thus, a traction force can be applied to the flat layer of material 3 by the rollers 4, 5.

In the presently shown embodiment, both the upper roller 4 and the lower roller 5 show an outer surface 11 with a corresponding surface structure (see also FIGS. 2 and 3). Namely, ridges 9 of the first of the rollers 4 will partially protrude into corresponding, neighbouring troughs 10 of the second of the rollers 5 and vice versa. This will be explained in detail in the following, in particular with reference to FIGS. 2 and 3.

Due to the design of the rollers 4, 5, in particular due to the design of the outer surfaces 11 of the rollers 4, 5, the sheet of material 3 that passes through the nip 6 will be corrugated. The corrugated sheet 7 of material leaves the processing nip 6 at its other side. The corrugated sheet 7 is fed to the product coil 8, on which the processed and corrugated sheet 7 of material is wound up. The corrugation of the corrugated sheet 7 is shown in FIG. 1 in an exaggerated way for illustrative purposes.

Albeit in the present example the outer surfaces 11 of both rollers 4, 5 show a fully structured outer surface 11, it has to be understood that it is also possible that only one of the rollers 4, 5 shows a structured outer surface 11; that one or both of the rollers 4, 5 show an only partially structured outer surface 11 (meaning that a part of the outer surface 11 of the respective roller(s) will show an essentially unstructured outer surface); and the like.

In FIG. 2, the nip 6 that is formed by upper roller 4 and lower roller 5 “as seen by the entering sheet of material 3” is shown in more detail. In other words, the view of FIG. 2 is perpendicular to the view of FIG. 1. As can be seen in FIG. 2 particularly well, the upper rollers 4, 5 both show a structured surface 11, comprising an alternating series of ridges 9 and troughs 10, where the pitch between two successive ridges 9 or the pitch between two successive troughs 10 remains essentially constant over the full width of the respective roller 4, 5. Furthermore, the amplitude of the surface structure, that is the difference in radius of the roller 4, 5 between the tops of the ridges 9 and the bottoms of the troughs 10 remains essentially constant over the full width of the respective roller 4, 5 as well.

As can be further seen in FIG. 2 and in more detail in FIG. 3, the arrangement of the ridges 9 and the troughs 10 is slightly offset on the two neighbouring rollers 4, 5, so that the ridges 9 and the troughs 10 partially intermesh with each other. In particular, usually the offset between the structure of the outer surface of the rollers 4, 5 is essentially equivalent to about half of the pitch 12 between two successive ridges 9 or two successive troughs 10.

Depending on the design of the rollers 4, 5, the sheet of material 7 that is leaving the nip 6 (i.e. the sheet of material 7 that is processed by apparatus 1 as indicated in FIG. 1) will show a corresponding surface structure.

It should be understood that the surface structure 11 and the placement of the rollers 4, 5 as shown in the present embodiment is only according to a typical example.

Different embodiments are likewise possible. For example, it is possible as well that only one of the rollers (for example the upper roller 4) shows a surface structure 11, comprising ridges 9 and troughs 10, while the other roller (for example the lower roller 5) shows an essentially unstructured outer surface. Similarly, the surface structure 11 on the two rollers 4, 5 may be different as well. As a nonlimiting example: the amplitudes 14 of surface structures 11 of the two rollers 4, 5 may be chosen differently.

In FIG. 3 the geometry of the surface structure 11 is shown in more detail. Only for completeness, it should be mentioned that due to the scale of FIG. 3 only a very limited number of ridges 9 and troughs 10 is shown. In reality, the number of ridges 9 and troughs 10 will be usually significantly larger. Furthermore, only those parts of the outer surfaces 11 of the neighbouring rollers 4, 5 that are forming the nip 6 can be seen in FIG. 3 due to the scale chosen.

The pitch 12 of the ridges 9 (the peaks or tips), which is the distance between two successive ridges 9 as measured in the axial direction of the corresponding roller 4, 5, is presently chosen to be about 1 millimetre. Since the surface structure 11, in particular the ridges 9 and the troughs 10 are arranged symmetrically, the distance 13 between a ridge 9 and the neighbouring trough 10, as seen in the axial direction of the respective roller 4, 5, will be half of the pitch 12, and will therefore be about 0.5 millimetres. In the presently shown example, the amplitude 14, which is the distance between a ridge 9 and a trough 10 as seen in in the radial direction of the respective roller 4, 5 is presently 1 millimetre as well. Therefore, the slant distance between a ridge 9 (peak) and the neighbouring trough 10 will be correspondingly larger. Presently, it can be calculated by the theorem of Pythagoras and reads about √{square root over (1²+0.52)}=1.12 (indicated lengths in millimetres).

Furthermore, the offset between the two surface structures 11 in the axial direction can be seen in FIG. 3 as well. Presently, the offset is chosen to be half of the pitch 12 between two neighbouring ridge 9, which is about 0.5 millimetres according to the present geometry. This way, a ridge 9 of the upper roller 4 will be axially aligned with a trough 10 of the lower roller 5 and vice versa.

According to an important aspect of the present invention, the flank angle 15, which is the angle that is enclosed between a flank 16, neighbouring a ridge 9, and a line that is arranged in a radial direction of the respective roller 4, 5 that is passing the tip of the ridge 9 will have a certain value. Due to the presently symmetrical design of the rollers' 4, 5 surfaces 11, the angle that is enclosed between the two flanks 16 that are neighbouring a ridge 9, is about twice the flank angle 15.

In the presently shown example (where FIG. 3 is not drawn to scale), the flank angle 15 is chosen to be about 9 degrees. In particular, a certain variation is possible. In particular, the flank angle 15 may be chosen to be between about 4 degrees and about 20 degrees. According to a preferred embodiment, the flank angle 15 may be chosen to be between about 8 degrees and about 10 degrees. However, different upper and lower limits are possible (including a combination of the indicated limiting values), for example about 5 degrees, about 6 degrees or about 7 degrees (in particular as a lower limit) or about 11 degrees, about 12 degrees, about 13 degrees, about 14 degrees, about 15 degrees, about 16 degrees, about 17 degrees, about 18 degrees or about 19 degrees (in particular as an upper limit).

It is particularly preferred that the flanks 16 will show a certain length that is straight, which means that it does not show a local surface curvature. The ridges 9 and the troughs 10 are preferably rounded essentially following a circular shape. Of course, it is to be understood that a different design is possible as well. In particular, the surface curve can be a spline or something else as well. In this case (but possibly in other cases as well), as the defining point of the flank 16, where one leg of the flank angle 15 is measured, the inflection point of the respective curve can be chosen (the line that is pointing in a radial direction may form the other leg of the flank angle 15). However, different definitions of the flank angle 15 are likewise possible. 

1-14. (canceled)
 15. Apparatus for crimping a sheet of material, the apparatus comprising: a first and a second facing crimping rollers defining a first and a second rotation axis, wherein at least one of the first and second crimping roller includes: a plurality of ridges, each ridge defining a first and a second flank and a tip, the first or the second flank forming a flank angle with a radial direction passing through the tip, wherein all ridges of the plurality form a flank angle comprised between about 4 degrees and about 20 degrees.
 16. Apparatus according to claim 15, wherein the ridges are distanced one to the other with a constant pitch.
 17. Apparatus according to claim 15, wherein said ridges have all substantially the same amplitude.
 18. Apparatus according to claim 15, wherein the first and second flank are symmetrical with respect to the radial direction passing through the tip.
 19. Apparatus according to claim 15, wherein the first or the second roller is realized in metal.
 20. Apparatus according to claim 15, wherein the other of the first and second crimping roller includes a plurality of ridges, the first and second rollers being arranged such that the ridges of the first roller substantially interleave with the ridges of the second roller.
 21. A method of manufacturing a crimped sheet for an aerosol-generating article, the method comprising the steps of: feeding a substantially continuous sheet of material to a set of crimping rollers, the set of crimping rollers comprising a first roller and a second roller, at least one of the first or second roller including a plurality of ridges; and crimping the substantially continuous web to form the crimped web by feeding the substantially continuous sheet between the first and second rollers in a longitudinal direction of the sheet of material such that the ridges of the first or second rollers apply a plurality of crimp corrugations to the substantially continuous sheet of material; wherein the ridges in the first or second roller defines a first and a second flank and a tip, the first or the second flank forming a flank angle with a radial direction passing through the tip, wherein the flank angle formed by all ridges of the first or second roller is comprised between about 4 degrees and about 20 degrees.
 22. A method of manufacturing an aerosol-generating article component, the method comprising the steps of: manufacturing a crimped sheet according to claim 21; gathering the crimped sheet to form a continuous rod; and cutting the continuous rod into a plurality of rod-shaped components, each rod-shaped component having a gathered crimped sheet formed from a cut portion of the crimped sheet, the crimp corrugations of the crimped sheet defining a plurality of channels in the rod-shaped component.
 23. The method according to claim 21, wherein the sheet of material is one of: a sheet of alkaloid containing material, a plastic sheet or a sheet including cellulose.
 24. The method according to claim 23, wherein the sheet of alkaloid containing material includes a homogenised tobacco sheet.
 25. A crimped sheet realized according to the method of claim
 21. 26. The crimped sheet according to claim 25, wherein the crimped sheet of material is one of: a sheet of alkaloid containing material, a plastic sheet or a sheet including cellulose.
 27. The crimped sheet according to claim 26, wherein the sheet of alkaloid containing material includes a homogenised tobacco sheet.
 28. An aerosol generating article comprising a portion of the crimped sheet of claim
 25. 